1. Field of the Inventive Concepts
The inventive concepts disclosed herein pertain generally to the field of aircraft display units that present information to the pilot of an aircraft.
2. Description of the Related Art
The continuing growth of aviation has placed increasing demands on airspace capacity and emphasizes the need for the best use of the available airspace. These factors, along with the accuracy of modern aviation navigation systems and the requirement for increased operational efficiency in terms of direct routings and track-keeping accuracy, have resulted in the concept of “Required Navigation Performance” (“RNP”) standards—statements of the navigation performance accuracy necessary for operation within a defined airspace. Some of these standards appear in an Advisory Circular (“AC”) published by the Federal Aviation Administration (“FAA”) and in a Document (“DO”) published by the Radio Technical Commission for Aeronautics (“RTCA”). For example, the FAA has published AC 120-29A entitled “Criteria for Approval of Category I and Category II Weather Minima for Approach,” and the RCTA has published DO-236B entitled “Minimum Aviation System Performance Standards: Required Navigation Performance for Area Navigation,” each of which is incorporated herein in its entirety. Other RNAV-related publications include AC 90-100A entitled “U.S. Terminal and En Route Area Navigation (RNAV) Operations” and AC 90-101A entitled “Approval Guidance for RNP Procedures with AR,” each of which is incorporated herein in its entirety.
Aircraft area navigation (RNAV) and required navigation performance (RNP) systems installed in aircraft may be designed to performance-based specifications that are defined in terms of quality factors such as accuracy, integrity, availability, continuity, and functionality. RNAV and RNP systems may allow an aircraft to fly a specific flight track between two waypoints, where each waypoint may be a defined as a three-dimensional point above or on the ground; the former could be a position defined by a latitude, longitude, and altitude, and the latter could be a surveyed position measured by latitude, longitude, and elevation such as, for example, the locations of a ground-based navigational aid, a landing threshold point, and/or a glide path intercept point.
In the past, the navigational capabilities of an aircraft were defined relative to ground-based navigation aids such as, for example, a Very High Frequency Omni-Directional Range (VOR) station or a Non-Directional Radio Beacon (NDB) station; however, with RNP, an airplane's navigational capability may be defined in terms of the performance and integrity of equipment installed onboard an aircraft. As such, a number of navigation solutions may be generated by the equipment such as a global navigation satellite system (or satellite navigation system including global positioning system (GPS)) and ground-based navigation aids employing Distance Measuring Equipment such as DME/DME, and/or VOR/DME. Each of these provides an aircraft with a certain degree of navigational precision/navigational capability. The higher the degree of navigational capability/performance, the more precisely the aircraft may be able to follow a pre-determined flight path, thereby reducing the separation between some routes and increasing airspace utilization. Also, improved navigational capability may allow a pilot of an aircraft to approach an airport in mountainous terrain that would otherwise not be permitted.
Measurements corresponding to RNP include estimated position uncertainty (EPU) and flight technical error (FTE). The former may be a value calculated by an aircraft's source of navigation data such as a flight management system (FMS) to indicate a level of quality of the aircraft's actual position, and the latter may be a degree of precision with which an aircraft may be flown either manually or on autopilot along a desired flight path. Two types of routes that RNP-capable aircraft may utilize include RNAV routes and RNP routes.
For RNAV routes, there may be a requirement that an aircraft's total system error (TSE) be within an RNAV boundary equal to one times the RNP value ninety-five percent of the time, where TSE is equal to the sum of EPU and FTE. For instance, for an RNAV 2.0 route (i.e., route required to have an RNAV performance is 2.0 Nautical Miles (nm), the pilot would be allowed an FTE of 1.5 nm if the EPU is calculated to be 0.5 NM. Having knowledge of the FTE available or allowable may enhance a pilot's ability to maintain the required navigational track within RNAV boundaries.
For RNP routes, there may be a requirement that an aircraft be flown within an RNP boundary equal to one times the RNP value ninety-five percent of the time. Another requirement includes the monitoring and alerting corresponding to a probability of failure to detect TSE larger than a second RNP boundary equal to two times the RNP value is no greater than 10E-5. For example, for an RNP 0.1 approach procedure, an aircraft will have to be flown within an RNP boundary of 607 feet (one times the RNP value of 0.1 nm) ninety-five percent of the time and equipped with monitoring and alerting corresponding to a second RNP boundary of 1,214 feet (two times the RNP value of 0.1 nm).
The flight path of RNAV and RNP routes may be comprised of a plurality of waypoints that are presentable in an image to the pilot. For example, waypoints may be depicted as three-dimensional objects as disclosed by Chiew et al in U.S. Pat. No. 7,965,202 entitled “System, System, [sic] Module, and Method for Presenting an Abbreviated Pathway on an Aircraft Display Unit,” which is hereby incorporated by reference in its entirety. Also, a deviation from an RNAV path and RNP path may be depicted as a course deviation indicator as disclosed by Barber in U.S. Pat. No. 7,782,229 entitled “Required Navigation Performance (RNP) Scales for Indicating Permissible Flight Technical Error (FTE),” a reference hereby incorporated by reference in its entirety.